The present invention relates to rotary power shears and in particular to an improved rotary shear design that is safe, easy to operate and inexpensive to manufacture.
Rotary power shears of the type to which the present invention pertains are known in the art and typically comprise a motor driven worm gear which extends axially from the end of the motor shaft and which in turn drives a shear wheel that rotates against a cooperating driven shear wheel. Material to be cut is fed between the shear wheels where it is cut and then passed below the motor housing which typically serves also as the handle for the tool.
The present invention seeks to provide an improved rotary shear design that provides better balance for better control of the cutting head. With conventional rotary shears, the motor housing either comprises the handle for the tool as noted or serves as a support for a handle which is typically fastened to the end of the motor housing opposite the cutting head. This arrangement creates an imbalance in the tool due to the extension of the gear box and cutting head assembly beyond the front end of the motor. In other words, the tool tends to feel "front-heavy" when operated. This in turn compromises the ease with which the tool can be controlled, particularly when used to make irregular-shaped or lengthy cuts. The present invention eliminates this disadvantage by providing a rotary shear design having a handle that extends above the motor housing and gear box and which supports the tool from the gear box at one end and the rear of the motor housing at the other. In this manner, the tool is almost perfectly balanced when held by the handle. In addition, the position of the handle serves to remove the operator's hand from the vicinity of the cutting head. This improves the safety of the tool and also insures that the user's hand will not interfere with cut material as it passes beneath the underside of the motor housing.
Additionally, the present rotary shear design eliminates the more expensive worm gearing used in prior art designs and instead utilizes less costly spur gearing to provide the necessary gear reduction to drive the shear wheels. Moreover, the entire gear mechanism is enclosed in a compact gear casing located forward of the motor in the lower front portion of the tool to balance the weight of the motor as described above. As will be more fully discussed in the description of the preferred embodiment, the compactness of the gear casing and cutting head assembly is in part due to the utilization of a single bracket member to support and bias together the shear wheels, provide a cover for the gear casing, and to also provide a bearing support for the stub shafts or pins on which the gears are journalled.
Further improvements in the design of the present rotary shear include an overload release clutch which is provided in the gearing mechanism to protect the tool against excessive torque loads, and a reverse capability which facilitates the removal of a jammed workpiece with minimum damage to the workpiece and also allows easy withdrawal of the tool from a workpiece when making a "blind" cut.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :